hwmon: (it87) Delete pwmN_freq files on driver removal

In commit f8d0c19a93cea3a26a90f2462295e1e01a4cd250 I forgot to delete
the pwmN_freq files on driver removal, here's the fix.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Riku Voipio <riku.voipio@movial.fi>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>

drivers/hwmon/it87.c

@@ -933,6 +933,9 @@ static struct attribute *it87_attributes_opt[] = {
 	&sensor_dev_attr_pwm1.dev_attr.attr,
 	&sensor_dev_attr_pwm2.dev_attr.attr,
 	&sensor_dev_attr_pwm3.dev_attr.attr,
+	&dev_attr_pwm1_freq.attr,
+	&dev_attr_pwm2_freq.attr,
+	&dev_attr_pwm3_freq.attr,
 
 	&dev_attr_vrm.attr,
 	&dev_attr_cpu0_vid.attr,